In an air conditioning system using a fluorine compound such as HFC134, which has been broadly employed, as refrigerant, lubricating oil such as refrigerating machine oil is mixed into refrigerant beforehand, the lubricating oil is separated from the refrigerant when compressed refrigerant temporarily stays in a discharge chamber of a compressor, and the separated lubricating oil is supplied to a crank chamber by urging the oil by a pressure difference between discharge pressure and suction pressure or intermediate pressure therebetween, thereby lubricating rolling part or slide part in a crank case.
In such a structure for supplying lubricating oil, the pressure difference between discharge pressure and suction pressure utilized for urging the lubricating oil becomes great, there is a case where the amount of supplied lubricating oil becomes too great, and therefore, for example, as described in Patent document 1, the flow rate of lubricating oil is suppressed by increasing the resistance of a flow path by inserting a pressure reducing member such as an aperture with a small diameter or a porous material into an oil supply passageway for the lubricating oil or by forming the oil supply passageway as a thin and long passageway.
In an air conditioning system using carbon dioxide as refrigerant, however, because the pressure difference between suction pressure and discharge pressure increases about five times as compared with a case of an air conditioning system using a usual refrigerant such as HFC134, in order to perform a forcible lubrication by urging lubricating oil by a pressure difference between discharge pressure and suction pressure in the refrigerant compressor using carbon dioxide refrigerant, it is necessary to supply the lubricating oil after suppressing the flow rate of the lubricating oil further greatly as compared with the case of usual refrigerant, and therefore, it is inevitable to form the aperture and the like, to be provided in the oil supply passageway as a pressure reducing member, as one which is very thin and long. However, if done so, clogging ascribed to foreign matters liable to occur.
Accordingly, as another measure, a structure is disclosed in Patent document 2 wherein an intermittent oil supply mechanism is formed on an oil supply passageway without using a pressure reducing member, thereby shortening a substantial oil supply time to control the amount of supplied oil. Although this structure is effective for preventing clogging ascribed to foreign matters, there is a problem that machining of a communication hole from an oil storage chamber and machining of a hole of a piston are troublesome.
Patent document 1: Japanese Utility Model Laid-Open 59-119992
Patent document 2: JP-A-11-241682